The invention relates to a method and an arrangement in a radio communication system in which a mobile station is operating. More in particular, the invention relates to a method and arrangement for determining if the mobile station is present in a specific area.
A problem that often arises in connection with mobile stations operating in a radio communication system is to determine if a certain mobile station is present in a specific area. One example scenario where this problem occurs is where a home base station, i.e. a private base station which can be connected to the public telephone network, is installed in the home of a public cellular network subscriber and the subscriber, using his or her mobile station, prefers to communicate via the home base station while at home and within the radio coverage area of the home base station instead of via the cellular network.
GB 2 282 735 describes a communication system in which a user carries a handset which communicates either via a home base station connected to a telephone network or via a cellular network when away from the home base station. Apart from the facility to transmit data and analog signals for call connection, identification and traffic purposes in its cellular mode, the handset also transmits low power narrow bandwith signals which identify the user. When the user comes in close proximity with the home base station, the identity signals are received by the home base station and triggers a switch to a second operation mode in which incoming calls to the user are routed via the telephone network and the home base station.
A handset which, according to GB 2 282 735, transmits a low power identification signal in addition to transmitting call related signals need to be equipped with at least two transmitters which increases the complexity and cost of the handset.
Furthermore GB 2 282 735 discloses how incoming calls are routed via the telephone network and the home base station after a change to the second operation mode. There is no disclosure relating to handing off a call established in the cellular network to the home base station.
U.S. Pat. No. 5,260,988 describes a dual mode cellular cordless portable radiotelephone which may either operate in a cordless telephone system or a cellular network. The radiotelephone preferentially selects the cordless system when in range of this system.
When the radiotelephone is operating in idle mode, i.e. powered on but no call established, in the cellular network, the radiotelephone monitors a first control channel transmitted by a base station belonging to the cellular network. The radiotelephone temporarily stops monitoring the first control channel for a certain time period. During this time period the radiotelephone scans for radiosignals from the cordless system. If the cordless system is found, the radiotelephone moves to the cordless system, otherwise monitoring of the first control channel is resumed.
U.S. Pat. No. 5,260,988 also discusses handing off an established call from the cellular system to the cordless system. However, U.S. Pat. No. 5,260,988 neither discloses what triggers the radiotelephone to try and change to the cordless system, nor how the radiotelephone is able to maintain the established call while scanning for radiosignals from the cordless system.
The general problem dealt with by the present invention is detecting whether a specific mobile station is present in a determined area.
The problem is solved essentially by a method wherein the mobile station transmits information identifying the mobile station on a radio channel allocated for communication between the mobile station and a first base station. When a detecting unit receives the transmitted identity information, the mobile station is registered as present in a determined area. The solution includes the necessary means for implementing the method in the radio communication system.
More specifically, the problem is solved in the following manner. A first radio channel is allocated for communication of control information and user data information between the mobile station and the first base station. The mobile station transmits the identity information repeatedly on the first radio channel. The detecting unit receives at least one occurrence of the transmitted identity information. The mobile station is registered as present in the vicinity of the detecting unit upon receipt of said at least one occurrence of the identity information.
A general object of the present invention is to provide a method and an arrangement enabling a detecting unit to detect whether a specific mobile station is present in the vicinity of the unit.
A more specific object of the invention is to provide such a mobile station presence detection method and arrangement which do not require the mobile station to include more than one transmitter.
Still another object is to provide a hand off method and arrangement wherein hand off of the mobile station from said first base station to a second base station is triggered when, using said mobile station presence detection method, the mobile station is detected as present within the coverage area of the second base station.
One advantage afforded by the invention is that it provides a mobile station presence detection method and arrangement which do not require the mobile station to include more than one transmitter.
Another advantage is that the invention enables a selective hand off method and arrangement wherein the decision to trigger hand off of a selected mobile station, communicating with a first base station in a first radio communication network, to a second base station, separate from the first radio communication network, is transparent to the mobile station and the first radio communication.
The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings.